In recent years, together with an electricity generation device such a photovoltaic generation device, an electricity storage device has been increasingly placed for each consumer. The electricity storage device charges when an amount of consumed electricity is smaller than an amount of generated electricity, and discharges when the amount of consumed electricity is larger than the amount of generated electricity, thereby enabling the consumer to efficiently use electricity generated by the electricity generation device.
It is assumed that a storage battery such as a lithium-ion battery is used as such an electricity storage device. The storage battery such as the lithium-ion battery has characteristics of deteriorating when charging or discharging excessively. Thus, for instance, the charge or discharge of the storage battery is managed so that a charging rate fails within a certain range (e.g., 20% to 80%).
In view of the above, to keep the charging rate of the storage battery in the certain range, a technique of performing electric power interchange between consumers has been proposed (e.g., refer to Patent Literature (PTL) 1). In the technique disclosed in PTL 1, the electric power interchange is performed according to an amount of electricity stored in the storage battery.